The present disclosure relates to subterranean operations and, more particularly, to apparatus and methods for monitoring and characterizing cement in a subterranean formation.
Performance of subterranean operations entails various steps, each using a number of devices. Many subterranean operations entail introducing one or more fluids into the subterranean formation. For instance, during the drilling and construction of subterranean wells, it may be desirable to introduce casing strings (“casing”) into the well bore. To stabilize the casing, a cement fluid or slurry is often pumped downwardly through the casing, and then upwardly into an annulus formed between the casing and the walls of the well bore. Once placed in the annular space, the cement composition is permitted to set therein, thereby forming an annular sheath of hardened, substantially impermeable cement that substantially supports and positions the casing in the well bore and bonds the exterior surface of the casing to the interior wall of the well bore. Once the cement sets, it holds the casing in place, facilitating performance of subterranean operations. These operations in which a casing is cemented into the well bore are sometimes referred to as primary cementing operations.
Other cementing operations (sometimes referred to as remedial cementing or squeeze cementing) involve pumping cement into a void space, crack, or permeable zone in a formation at a desired location in the well. Remedial and squeeze cementing operations may be performed at any time during the life of the well: drilling, completions or producing phases. In order to be effective, these types of cementing operations generally require accurate placement of the proper amount of cement in a desired location.
Maintaining fluid pressure in the well bore, accurately placing cement in the desired location(s) in the well bore, and ensuring complete curing of the cement in the desired location, among other things, are often critical to these and other subterranean operations in a well bore. However, fluids placed in a well bore, including the cement slurry, may migrate or flow into another portion of the subterranean formation other than their intended location, for example, in an area of the formation that is more porous or permeable. Fluid loss may result in, among other problems, incomplete or ineffective treatment of the formation, increased cost due to increased volumes of fluid to complete a treatment, and/or environmental contamination of the formation. While treatment fluids are often formulated and wells are often constructed so as to reduce the likelihood or amount of fluid loss into the formation, fluid loss still may occur, particularly in damaged or highly permeable areas of a subterranean formation or well bore.
Conventional methods of detecting fluid loss typically involve measuring the amount of fluid pumped into the well bore and comparing that with the amount of fluid circulated out of the well bore. However, such methods are usually only performed after the operation using the fluid has been completed, and do not give an operator enough information during the operation to make adjustments to attempt to compensate for the fluid loss or otherwise remedy whatever is causing the loss of fluid. This may require performing the same treatment or operation on the same well bore multiple times until it can be performed without significant fluid loss. Moreover, such methods typically are not capable of identifying the specific fluid that was lost into the formation, the identity of which may be important in order to compensate for the lost fluid and/or remedy or prevent additional problems (e.g., formation damage, environmental problems, etc.) that may result from the loss of particular fluids into the formation.
While embodiments of this disclosure have been depicted and described and are defined by reference to example embodiments of the disclosure, such references do not imply a limitation on the disclosure, and no such limitation is to be inferred. The subject matter disclosed is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those skilled in the pertinent art and having the benefit of this disclosure. The depicted and described embodiments of this disclosure are examples only, and not exhaustive of the scope of the disclosure.